Antenna system

ABSTRACT

An antenna system adapted to operate over relatively wide scan angles is disclosed. The antenna system includes a means for providing a control signal indicative of the relationship between a desired beam deflection angle and a predetermined beam deflection angle, and means, responsive to the control signal, for causing the antenna to operate in the TE11 mode when the desired beam deflection angle is less than the predetermined beam deflection angle thereby to generate a broadside antenna radiation pattern, or the TM01 mode when the desired beam deflection angle is greater than or equal to the predetermined beam deflection angle thereby to generate an end fire antenna radiation pattern. The latter means includes a power divider having a pair of output ports, phase shifter means for providing either O* or 180* phase shift between the energy passing through such pair of output ports selectively in accordance with the control signal, and a radiating aperture section including a circular waveguide coupled to the pair of output ports and dimensioned to support either the TE11 mode or the TM01 mode. When such phase shift is 0* the antenna operates in the TE11 mode and when such phase shift is 180* the antenna operates in the TM11 mode.

United States Patent 1 1 1 3,909,829 Dal 1 1 Se t. 30 1975 1 ANTENNA SYSTEM wide scan angles is disclosed. The antenna system inludes a means for rovidin a control si nal indica- 75-1 t: Ed'd.Dal',Slb- Ma::. C P c l 1 nvcn or J m my 88 tive of the relationship between a desired beam deflec- [73] Assignee: Raytheon Company. Lexington. tion angle and a predetermined beam deflection angle MH and means, responsive to the control signal, for caus- 0 1 z z TE mode when the 22 Fl d: l 30, 1973 m thc mtcnn 1 to operite 1n the l l 3 desired beam deflection angle is less than the prede- [2 l Appl. No.: 383,849

[52] US. Cl 343/100 SA; 343/777; 343/854 [51} Int. Cl. HOlq 3/24 [58] Field of Search 343/100 SA. 854. 100 AD, 343/16 LS. 777

[56] References Cited UNITED STATES PATENTS 3222 677 12/1965 Fink 343/16 LS 3 4l9 866 12/1968 Holley, .Ir 343/117 R Prinau'y E.\'uminer-Riehard A. Farley AXSiAItHII liruminer-Richard E. Berger Attorney Agent. or FirmRichard M. Sharkansky; Philip J. McFarland; Joseph D. Pannone [57] ABSTRACT An antenna system adapted to operate over relatively termined beam deflection angle thereby to generate a broadside antenna radiation pattern, or the TM mode when the desired beam deflection angle is greater than or equal to the predetermined beam dc flection angle thereby to generate an end fire antenna radiation pattern. The latter means includes a power divider having a pair of output ports, phase shifter means for providing either 0 or 180 phase shift between the energy passing through such pair of output ports selectively in accordance with the control signal, and a radiating aperture section including a circular waveguide coupled to the pair of output ports and dimensioned to support either the TE, mode or the TM mode When such phase shift is 0 the antenna operates in the TE mode and when such phase shift is 180 the antenna operates in the TM mode.

4 Claims. 3 Drawing Figures TRANSMITTER RECE|VER CONTRO LLER /5 STEERING COMPUTER COMPARATOR REGISTER US. Patent sfipt. 30,1975 Sheet 1 of2 3,909,829

/ TRANSMITTER CONTRO LLER /5 BEAM STEERING COM PUTER COMPARATOR REGISTER Sheet 2 of 2 9 mm @200 0 mmtb 33mm 20mm US. Patent Sept. 30,1975

ANTENNA SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to antenna systems and more particularly to systems of such sort which are adapted to operate over relatively wide scan or deflection angles.

As is known in the art, a collimated beam of radio frequency energy may be formed and steered by controlling the amplitude and phase of the energy radiated from each one of a plurality of antenna elements in an array thereof. The radiation pattern of a typical array includes, in addition to a desired main lobe, several side lobes. Such side lobes generally are undesirable because they reduce the amount of energy in the main lobe.

As the scan or deflection angle of the main lobe is increased from boresight, the energy in the side lobes increases, with a concomitant decrease of energy in the main lobe. In an airborne radar system, for example, it is generally desirable that an antenna array system be operable over a relatively wide range of scan angles to permit operation for both terrain avoidance and collision avoidance. One known technique used to increase the range of scan angles is to use, in combination, a mechanical gimbal drive mechanism and an electronic phased array antenna which is mounted to the gimbal system. The gimbal drive mechanism is arranged to extend the scan angle range of the phased array antenna. The use of such combination, while adequate in some airborne applications, has been sometimes found to be inadequate because such system includes a relatively slow responding mechanical drive mechanism.

SUMMARY OF THE INVENTION With this background of the invention in mind it is therefore an object of this invention to provide an improved antenna system which is adapted to operate over relatively Wide scan angles.

This and other objects of the invention are attained generally by providing an antenna system including means for providing a control signal indicative of the relationship between a desired beam deflection angle and a predetermined beam deflection angle, and means, responsive to the control signal, for causing the antenna to operate in a selected one of a plurality of possible operating modes, such mode being selected in accordance with the relationship between the desired beam deflection angle and the predetermined beam deflection angle.

In a preferred embodiment a phase array antenna operates in a selected one of two possible modes, one such mode providing a broadside antenna radiation pattern and the other such mode providing an end fire antenna radiation pattern. When the beam steering signals direct the beam of radiation to deflection angles less than some predetermined angle a broadside antenna radiation pattern is generated by the antenna, and when the beam steering signals direct the beam of radiation to deflection angles greater than or equal to such predetermined angle an end fire antenna radiation pattern is generated by the antenna.

In such embodiment one of the plurality of antenna elements includes: A power divider having a pair of output ports, means for providing either or 180 phase shift between the energy passing through such pair of output ports selectively in response to the control signal and a radiating aperture section including a circular waveguide coupled to the pair of output ports. The circular waveguide is dimensioned such that its cutoff frequency is lower than that of either the TE, mode or the TM mode of the radio frequency energy propagating therethrough. When the relative phase shift between the energy passing through the pair of output ports is 0 the phased array antenna operates in the TE mode and a broadside radiation pattern is developed by the antenna. When the relative phase shift between the radio frequency energy passing through the pair of output ports isthe phased array antenna operates in the TM mode and an end fire radiation pattern is developed by the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing features of this invention, as well as the invention itself, may be fully understood from the following detailed description read together with the accompanying drawings, in which:

FIG. 1 is a simplified sketch of an airborne phased array radar system according to the invention, such radar system being adapted to generate either a broadside antenna radiation pattern or an end fire antenna radiation pattern selectively in accordance with the relationship between a desired radiation beam deflection angle and a predetermined radiation beam deflection angle;

FIG. 2 is a simplified sketch of the phased array radar system of FIG. 1 including a plurality of antenna elements to radiate a collimated beam of radio frequency energy and to receive echo signals from targets illuminated by such radiated energy; and

FIG. 3 is an isometric drawing, greatly simplified and exploded, of one of the antenna elements of the phased array radar system of FIG. 2 according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I it may be seen that an airborne phased array radar system 10 is adapted to produce either a broadside antenna radiation pattern 6 or an end fire antenna radiation pattern 8 selectively in accordance with the relationship between a desired radiation beam deflection angle and a predetermined radiation beam deflection angle in a manner to be described hereinafter. The beam deflection angle 0 is here defined as the angular deviation from the boresight axis 7 of the antenna. As shown in FIG. 1, radiation pattern 6 has approximately a 0 deflection angle.

Referring now to FIG. 2 it may be seen that the phased array radar system 10 according to this invention includes a number of fixed antenna elements 11. The antenna elements 11 may be mounted in any conventional manner (not shown in detail) to form a space fed planar array antenna. As is known, such an arrange ment permits radio frequency energy from a feed horn 17 to be collimated in a beam and directed as desired in accordance with digital signals supplied by a beam steering computer 15. Also, echo signals returning to the individual antenna elements 11 of the antenna array 10 are focused to the feed horn 17 in accordance with digital signals supplied by beam steering computer 15. The feed horn 17 is connected in any conventional manner, as by waveguide (not numbered) to a transmitter/receiver 19. The operation of the transmitter/- receiver 19 and the beam steering computer is con trolled by conventional controller 21.

As will be described in detail hereinafter, the beam of radiation generated by the antenna will have a broadside antenna radiation pattern 6 (FIG. 1) or an end fire antenna radiation pattern 8 (FIG. 1 The radiation pattern is selected in accordance with the relationship between the desired beam deflection angle, as controlled by the beam steering computer 15, and a predetermined beam deflection angle, here say 30 from boresight axis 7. Such predetermined beam deflection angle, which may be varied within wide limits, may be selected so that the level of the antenna gain (as the main beam is deflected from boresight axis 7 during the broadside antenna radiation pattern mode of operation) is always above a desired level as determined a priori. A digital storage register 16, of conventional design, is provided to store a digital signal representative of the predetermined beam deflection angle 30. A comparator means 18 is provided to compare the desired beam deflection angle signal produced by beam steering computer 15 with the predetermined beam deflection angle signal stored in storage register 16. Such comparator means 18 is of conventional design and here develops a control signal on line 20. When the desired beam deflection angle, as commanded by the beam steering computer 15, is greater than, or equal to, the predetermined deflection angle, as stored in register 16, the control signal on line 20 selects, in a manner to be described, an end fire radiation mode for the antenna. When the desired beam deflection angle is less than the predetermined beam deflection angle the control signal on line 20 selects, in a manner to be described, 21 broadsideantenna radiation mode for the antenna.

Referring now also to FIG. 3, an exemplary one of the antenna elements 11 is shown in detail to include a phase shifter section 23, a mode selection section 25 and a radiating aperture section 27. The phase shifter section 23 in this particular embodiment has disposed within a rectangular waveguide 29 three serially arranged ferrimagnetic toroids 31a, 3 lb, 310, sometimes referred'to as ferrite phase shifters 31a, 3 lb, 31c designed to operate in response to a three bit binary signal supplied by beam steering computer 15. Obviously, however, the number of toroids or phase shifters may be changed without departing from the inventive concepts. A different bit of the three bit binary signal is supplied to a different one of the three identical current drivers collectively referred to as current driver, 13." A different one of the current drivers is coupled to a different one of the ferrimagnetic toroids 31a to cvia current drive cables 33a to c as shown. The toroids 31a to 310 are separated from each other and in a conventional manner by insulating spacers 35a to c as shown. Here such spacers 35a to c are magnesium titanite di electric spacers. A conventional support structure (not shown) fastens such spacers and toroid 310 within waveguide 29. An impedance matching device 37 is coupled to waveguide section 29. Such impedance matching device 37 is shown and fully described in U.S. Pat. application Ser. No. 369,028, Waveguide Device, Jerome D. Hanfling, inventor, filed June ll, 1973 and assigned to the same assignee as the present invention.

Mode selection section 25 includes a three port power divider 38. Such power divider 38 includes an input port 40 which is coupled to the phase shifter section 23 by means of suitable mounting flanges (not numbered). The power divider 38 includes a pair of output ports 42, 44 formed by a pair of rectangular waveguide sections. Such power divider 38 may be substantially a waveguide hybrid junction described in U.S. Pat. No. 3,281,720, S. B. Cohn, issued Oct. 25, 1966. Here, however, output sections 49, 51 of such hybrid junction extend beyond the resistive material 47, as shown, for reasons to be apparent. It is understood, however, that other power dividers may be used such as an E-plane forked hybrid T (as described in l.R.E. Transactions on Microwave Theory and Techniques, December 1955, by W. K. Kahn, pg. 52) with the H- plane port thereof (designated as port 3 in such article) properly terminated by a suitable load material. Power divider 38 provides equal power division of energy entering input port 40 between the two output ports 42, 44. Disposed within the pair of waveguide sections forming the output sections 49, 51 are ferrimagnetic phase shifting rectangular toroids 46, 48. The toroids 46, 48 are held within the rectangular waveguide forming ouput sections 49, 51 by engagement with the opposing wide walls of such waveguide. That is, the opposing wide walls provide spring loading engagement with the toroids 46, 48. This engagement thereby results in an electrical and a mechanical contact between the toroids 46, 48 and the rectangular waveguides when the power divider 38 is assembled. A wire 50 passes through toroid 46 and a wire 52 passes through toroid 48. Wires 50, 52 are connected to a current driver 54 here affixed to and mounted beneath mode selection section 25. The current driver 54 is actuated by the control signal on line 20. When the beam steering computer 15 (FIG. 2) commands a beam deflection angle greater than or equal to 30 a control signal is developed on line 20 enabling the current driver 54 to supply current through the toroids 46, 48 via wires 50, 52. The current in such wires 50, 52 flows in the direction indicated by the arrows (not numbered). It is noted that, as shown, such current flow is through toroid 46 from right to left and is through toroid 48 from left to right. Further, the toroids 46, 48 and the current driver 54 are arranged and designed such that when the current flows in the direction indicated by the arrows a phase shift is produced in each one of the toroids 46, 48. Therefore, because of the opposite direction in current flow in each one of the toroids 46, 48 the radio frequency energy passing through the output ports 42, 44 of the power divider 38 from input port 40 will have a relative phase shift therebetween. When the beam steering computer 15 produces beam steering signals for commanding the beam of radiation to deflection angles less than 30 the control signal on line 20 causes current driver 54 to become disabled so that no current is allowed to flow through wires 50, 52. In the absence of such current the relative phase shift between the radio frequency energy passing through output ports 42, 44 is therefore 0.

Radiating aperture section 27 is a section of circular waveguide dimensioned such that its cutoff frequency is lower than either the TE modeor the TM mode of the radio frequency energy propagating therethrough. The radiating aperture section 27 is fastened to the mode selection section 25 by conventional mounting flanges (not numbered). In operation, when the electric fields of the radio frequency energy passing through output ports 42, 44 to radiating aperture sec tion 27 are equal in amplitude and phase, such fields combine in the circular waveguide of the radiating ap erture section 27 so that the TE mode is supported therein. When the electric fields of the radio frequency energy propagating through such output ports are equal in amplitude but have a 180 relative phase shift therebetween such electric fields combine in the circular waveguide of the radiating aperture section 27 so that a TM mode is supported within such circular waveguide section. Therefore, when the beam steering computer 15 (FIG. 1) produces signals to direct the beam of radiation to deflection angles less than 30 the relative phase shift between the energy passing through the pair of output ports 42, 44 is and the phased array antenna operates in the TE mode, and such antenna develops a broadside radiation pattern 6 (FIG. 1). When the beam steering computer 15 produces beam'steering signals for directing the beam to deflection angles greater than or equal to 30 the relative phase shift of the radio frequency energy passing through the pair of output ports is 180, the phased array antenna operates in the TM mode, and such antenna develops an end fire radiation pattern, 8 (FIG. 1).

While the described embodiment of this invention is useful to an understanding thereof, it will be immediately apparent to those having skill in the art that the concepts of the invention may be applied to the design and construction of antenna systems having different characteristics than the illustrated embodiment. For example, While a space fed phased array antenna system has been shown, a corporate feed phased array antenna system may be used in place thereof. Also, the antenna system may be readily adapted for use in com munication applications such as satellite communication systems. Still further, while a 30 threshold was selected in the particular embodiment described herein, any other suitable angle could have been chosen and stored in register 16. While two 90 phase shifters were used in the mode selection section 25, it is now readily apparent that a single 180 phase shifter may have been substituted in place thereof. It is felt therefore that the invention should not be restricted to its disclosedembodiment but rather should be limited only by the spirit and scope of the following claims.

What is claimed is:

1. An antenna system, comprising:

a. means for providing a control signal indicative of the relationship between a desired beam deflection angle and a predetermined beam deflection angle; and I b. means, responsive to the control signal, for causing the antenna to operate in a selected one of a plurality of possible operating modes, such mode being selected in accordance with the relationship between the desired beam deflection angle and th predetermined beam deflection angle including means for causing one mode of such plurality of possible operating modes to produce a broadside antenna radiation pattern and another one of such modes to produce an end fire antenna radiation pattern.

2. The antenna system recited in claim 1 wherein the operating mode producing the broadside antenna radiation pattern is the TE, mode and the operating mode producing the end fire antenna radiation pattern is the TM mode.

3. The antenna system recited in claim 1 wherein the control signal responding means includes:

a. a power divider having a pair of output ports;

b. means, responsive to the control signal, for providing either a 0 or phase shift between the radio frequency energy passing through the pair of output ports selectively in response to the control signal; and

c. a radiating aperture section including a circular waveguide coupled to the output ports, such Waveguide being dimensioned with a cutoff frequency lower than that of either the TE mode or the TM mode of the radio frequency energy propagating therethrough.

4. The antenna system recited in claim 3 wherein the power divider is dimensioned to divide the radio frequency energy passing therethrough equally between the pair of output ports. 

1. An antenna system, comprising: a. means for providing a control signal indicative of the relationship between a desired beam deflection angle and a predetermined beam deflection angle; and b. means, responsive to the control signal, for causing the antenna to operate in a selected one of a plurality of possible operating modes, such mode being selected in accordance with the relationship between the desired beam deflection angle and the predetermined beam deflection angle including means for causing one mode of such plurality of possible operating modes to produce a broadside antenna radiation pattern and another one of such modes to produce an end fire antenna radiation pattern.
 2. The antenna system recited in claim 1 wherein the operating mode producing the broadside antenna radiation pattern is the TE11 mode and the operating mode producing the end fire antenna radiation pattern is the TM01 mode.
 3. The antenna system recited in claim 1 wherein the control signal responding means includes: a. a power divider having a pair of output ports; b. means, responsive to the control signal, for providing either a 0* or 180* phase shift between the radio frequency energy passing through the pair of output ports selectively in response to the control signal; and c. a radiating aperture section including a circular waveguide coupled to the output ports, such waveguide being dimensioned with a cutoff frequency lower than that of either the TE11 mode or the TM01 mode of the radio frequency energy propagating therethrough.
 4. The antenna system recited in claim 3 wherein the power divider is dimensioned to divide the radio frequency energy passing therethrough Equally between the pair of output ports. 